Primary load-bearing structures in aircraft are typically fabricated from a number of discrete parts that are joined together, as by welding, riveting, or other processes, to form the desired structure. The transfer of loads from one part to adjoining parts within the assembly is determined by the joining techniques used, and considerable effort is often invested in analyzing such load transfers and designing the structure to optimize the load transfers. In particular, it is often desirable in the design of aircraft structures to provide a "fail safe" structure whereby if the primary load path fails because of failure of a part or of a juncture between two parts along the primary load path, there is at least one alternate load path capable of safely providing the requisite load limit capability of the structure. Fail safety is one means of demonstrating compliance with airworthiness standards per Federal Aviation Regulations section 25.571.
The cost of fabricating a load-bearing structure can potentially be reduced by employing monolithic fabricating techniques such that discrete parts are consolidated into a single integral structure, thereby eliminating the necessity of fabricating multiple parts and joining the parts together. Typically, when monolithic structures are employed, however, no effort is made to provide multiple or alternate load paths.